Hyperthermia has promise as a means of cancer therapy in combination with radiotherapy and chemotherapy for tumors which can be effectively heated. The molecular effects of hyperthermia are not well understood, in particular the target (if there is a single one) of hyperthermia and the molecular basis of thermotolerance are not known. These two problems are intimately related since thermotolerance is probably due to protection or stabilization of the target. The specific aims of this proposal are to determine the identity of the thermolabile protein of the nuclear matrix and nuclei that denature at the transition temperature (Tm = 46 degrees C for V79 cells) of the critical target by thermal gel analysis. If these proteins constitute the critical target, then chemical sensitizers to hyperthermia that increase the protein/DNA ratio of isolated nuclei from heated cells and protectors that lower this ratio should affect their thermostability, (defined as the denaturation temperature Tm). In addition, we will determine if nuclear matrices from thermotolerant cells are more stable, and if exogenous HSC7O, which translocates to the nucleus during hyperthermia, can stabilize the nuclear matrix proteins (i.e. increase Trn) or facilitate the removal of excess nuclear proteins of isolated nuclei of heated cells. The reason that human cells are more resistant to hyperthermia than rodent cells at temperatures greater than 41 degrees C is unknown. We will determine if this is due to greater stability of cellular proteins of human cells and if so, if the nuclear matrix from human cells is more stable than that from rodent cells. These experiments will help determine if the denaturation of nuclear matrix proteins is a form of thermal damage that occurs during hyperthermia. The long term goal is to apply the technique of thermal analysis, that is the measurement of cellular protein denaturation by DSC and other physical techniques, to the problem of understanding thermal damage in mammalian cells and tissue. Thermal analysis has potential as a means of analyzing and predicting the thermostability, hence sensitivity to hyperthermia, of normal and tumor tissue.